Bourgas is high risk flight so Border Force routinely check. I’m not sure if Cardiff has a overhead x-Ray machine but Border Force usually screen the bags airside. If they suspect something they may have a look inside and then put it back on the belt. So when he walked into the Green Channel the Officers will be there to say a polite hello “do you have anything to declare?” Also they can screen bags in the green channel with a x-Ray machine. They’d arrest and prosecute with the aid of the NCA Border Crime teams. The only airport screening will be done at departure airport and if it’s hold luggage then as long as it doesn’t go bang at 40,000ft then they’ll be no reason the bag won’t travel i.e. firearms are routinely carried in the hold. The Bulgarian Customs wouldn’t have stopped the bag as all the stuff would be lawful there. No CWL airport security staff involved as they don’t have any power to open bags without the consent of the owner. If owner isn’t there they’ll contact Border Force or the Police. For international stuff Border Force has primacy for a few reasons but mainly they don’t require a warrant or permission from the owner to open the bag. Hence if your bag is delayed and you submit a declaration that you have nothing to declare, you’ll find a nice letter from Border Force saying your 1000 fags have been seized as you’re over your 200 Allowance when it’s delivered to your house by the airline.